In most conventional techniques of freeze drying, the product is frozen into powder or flake form and transported through a heating chamber to remove the moisture. When using direct heat, the chamber and all its contained structure becomes heated and the product may be damaged by partial melting or surface crusting, and much flavor is often lost due to chemical changes caused by the heating. As a result, it is impractical to freeze dry certain products by the heat method. Further, the process is lengthy and may take from eight to twelve hours or even longer, to produce a batch of powdered product. Often the apparatus must be shut down after a batch is completed, in order to remove the product and service the apparatus for subsequent use.
Moisture removal has also been a problem and condensors require frequent servicing for ice removal. In some systems, the process must be stopped to remove ice and return the heat exchange equipment to the proper temperature balance.
The process is thus complex and expensive and it is economically impractical to utilize freeze drying for a wide variety of products. Since many products which normally have a limited shelf life, or are bulky to store, could be stored easily for extended periods in dry powder form, a low cost and rapid freeze drying technique would be very desirable.